An NDE technique wherein an ultrasonic beam passes through a coating and substrate and provides a signal from the back wall. The signal is detectable by a sensor. The height of this backwall echo depends on the discontinuity in impedance from the sprayed coating to the substrate. Bonding flaws can be easily seen by the weakening of the back wall echo.
A synonym for supercooling.
In castings, the removal and repair of discontinuities to raise the quality level of the casting beyond that which can be economically achieved by good foundry practice.
Annealing carried out at subatmospheric pressure.
A casting in which metal is melted and poured under very low atmospheric pressure; a form of permanent mold casting where the mold is inserted into liquid metal, vacuum is applied, and metal drawn up into the cavity.
The deposition of thin films and coatings using a vacuum environment and an atomic or molecular condensable vapor source. The vacuum environment reduces gas particle density, limits gaseous contamination, establishes partial pressures of inert and reactive gases and controls gas flow. The gaseous environment can be partially ionized plasma, and the vapor source can be of PVD or CVD.
A furnace that uses low atmospheric pressures instead of the protective gaseous atmosphere used by most heat-treating furnaces. They are categorized as hot wall or cold wall depending on the location of the heating and insulating components.
Vacuum Plasma Spraying
Plasma spraying carried out in a chamber which has been evacuated to a low partial pressure of oxygen. It is then usually partially backfilled with argon to avoid the possibility of forming a glow discharge.
A chemical element, atomic number 23, which inhibits grain growth during heat treatment and which improves the strength and toughness of hardened and tempered steels. Additions up to .05% increase hardenability, whereas larger amounts tend to reduce hardenability due to the formation of carbide. It is also utilized in ferrite/pearlite microalloy steels to increase hardness through carbonitride precipitation strengthening of the matrix.
A way of displaying results from a CFD analysis, where the velocity of each particle is visualized with an arrow. Since the arrow represents velocity it has a direction and magnitude (the length of the arrow indicates the relative magnitude).
A discontinuity on the surface of a casting—appearing as a raised, narrow, linear ridge—that forms upon cracking of a sand mold or core caused by the expansion of the sand during the filling of the mold with molten metal.
Vickers Hardness Test
A microindentation hardness test that employs a 136° diamond pyramid indenter (Vickers) and variable loads—enabling the use of a single hardness scale, the range of which spans from very soft lead to tungsten carbide. Also known as the diamond pyramid hardness test.
A continuous-type furnace consisting of two sets of rails, one stationary and the other movable. Only the work being processed has to be heated because trays or fixtures are not needed.
A quench in that uses water as its quenchant. The major disadvantage of water quenching is its poor efficiency at the beginning, or hot stage, of the quenching process.
Loss of material from a surface by means of relative motion between it and another body.
Skin exposed too long to the ultraviolet rays of welding or melting arcs will burn as in a sunburn. Though temporary blindness can result, it is not permanent, as is popularly believed.
A compound layer that forms as a result of the nitriding process.
X-Ray Diffraction (XRD)
A surface science technique for crystalline structure analysis of materials. Widely used both in the research and industrial area. Analyzed depth: up to 10 micrometers.
X-Ray Photoelectron Spectroscopy (XPS)
An electron beam technique applied for the identification of near-surface elements and the analysis of chemical state. Widely used in thin film science. Analysis depth: a few Angstroms.
The lowest amount of stress in a material at which an increase in strain occurs without an increase in stress. If there is a decrease in stress after yielding, a distinction may be made between upper and lower yield points. The yield point is usually less than the maximum attainable stress.